In late 1997, the chambers inside the pyramid of the Pharaoh Menkaure at Giza were closed to visitors for cleaning and repair due to moisture exhaled by tourists, which raised its humidity to such levels so that salt from the stone was crystallizing and fungus was growing on the walls.

a. due to moisture exhaled by tourists, which rised its humidity to such levels so that salt from the stone was crystallizing
b. due to moisture that tourists had exhaled, thereby raising its humidity to such levels that salt from the stone would crystallize
c. because tourists were exhaling moisture, which had raised the humidity within them to levels such that salt from the stone would crystallize
d. because of moisture that was exhaled by tourists raising the humidity within them them to levels so high as to make the salt from the stone crystallize
e. because moisture exhaled by tourists had raised the humidity within them to such levels that salt from the stone was crystallizing

Doubt 1:
In OE for options C and D, it is mentioned that "them" in C and D seems to refer to tourists. But OE for E says that "them" in E clearly talks about chambers.
My understanding for this is as below reasons can you please confirm if my analysis is correct ?

In E : "exhaled by tourists" is a modifier that is modifying moisture and so the sentence "moisture had raised the humidity within them" is the sentence and so it is more clear that "them" refers to chambers.

In D: "tourists raising the humidity within them" "raising the humidity with in them" modifies "tourists". Hence, it looks like "them" refers to "tourists".

Not sure of the case with C.

Doubt 2:
In option A, idiom "such levels so that" is used. Is this correctly used ?

Doubt 3:
It is mentioned that "due to" is used imprecisely to express causal relation. Can you please eloborate on how "due to" can be used effectively to express these relations?

You analysis is fine. I agree with Marcab above that pronoun usage here is based on the sentence construction (tourist (subject of the clause) ....and hence the pronoun 'them' refers back to 'tourists' and not chambers and you can check if replacing 'due to' with 'caused by' still makes sense

more about due to VS because--- Due to modifies Nouns only and Because modifies Clauses. Due to will show direct causal relation to the Noun

eg-- From the helicopter, I saw a 6-mile long traffic jam, due to an overturned truck --'due to' modifies noun JAM caused directly by the overturned truck.

eg--I came late to the meeting, due to the traffic --The usage is INCORRECT since 'due to' modifies noun Meeting and the traffic does not cause the meeting (not a direct causal relation)
to correct it we will use because.
I came late to the meeting, because of the traffic. Here Because modifies the entire previous clause 'I came late to the meeting'

HTH
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Can someone edit this option. In Option E, it should "WITHIN" instead of "WITH".

I chose option D, just because of this small typo.
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